1. Field of the Invention
This invention relates to leaf springs made of a composite, fibre reinforced resin, material. More particularly, the invention relates to the provision of means by which another member or component can accurately be located relative to a spring.
For example, in automotive applications a leaf spring will usually require an axle to be secured to it at or near its centre. Such securing will normally be carried out by a clamp arrangement embracing the spring, but this does not provide location of the axle longitudinally of the spring. This has been done by a hole drilled through the spring to receive a bolt or the like, but unless the disposition of such a hole is carefully chosen it can affect the properties of the spring. In any event, it is inconvenient to have to drill a hole through the spring in an additional manufacturing operation. A further situation where some form of locating means for a spring is required is if an assembly of two or more leaf springs is used. The individual springs will typically require to be held in fixed positions relative to one another at one point along their lengths. It is the object of the present invention to provide an improved means whereby such location can be achieved.
2. Summary of the Invention
According to one aspect of the invention, I provide an assembly comprising a leaf spring of composite material, clamping means, and a component secured to the spring by said clamping means, characterised by a locating element having a head portion extending into a depression in said spring, said head portion and depression having shallow sloping walls, and a body portion co-operating with said component, to determine the position of said component relative to the spring.
The provision in the spring of a shallow, sloping walled, depression has a minimum effect on the properties of the spring. Further, since composite springs are typically manufactured by a moulding process, in which resin impregnated fibres are subjected to heat and pressure in a mould to cure the resin and form the finished spring, such a depression can easily be provided in the spring in manufacture. Drilling or other operations on the spring are not required subsequent to the moulding process. When the component is clamped to the spring, the locating element provides adequate security against relative movement, despite its engaging in only a shallow depression in the spring.
The head portion of the locating element, and the depression in the spring, may be of part-spherical shape. Alternatively, the head portion of the locating element could have a flat top, and the depression in the spring have a flat bottom.
When a component is secured by clamping means to a composite leaf spring, it is usual to arrange for relatively large areas of clamped surfaces of the component and spring, and a load distributing element of rubber or plastics material may be interposed between these surfaces. One problem that occurs in service with such an arrangement is that dirt can penetrate between the clamped surfaces and lead to wear from abrasion as the spring flexes. Thus, selection of a material for the load distributing element must be carried out very carefully if it is to perform satisfactorily. The material must be soft enough to spread the load into the composite material of the spring, as loads can be very high if elements such as U-bolts are used as the clamping means, and if such loads are not satisfactorily spread fatigue cracks can propogate into the spring. Conversely, if the material is too soft, the element becomes compressed and again will not perform any load spreading function. The abrasion resistance of the material must be good because of the abrasion effect referred to above.
In an assembly comprising an element of a resilient material interposed between the spring and component, the invention provides that the body portion of the locating element may extend through an aperture in the resilient element. If the resilient element is secured to the spring by an adhesive, which is desirable because it prevents dirt entering between the surface of the spring and the resilient element, the resilient element will serve to retain the locating element in engagement with the spring. This facilitates assembly of the spring and component.
The resilient element preferably comprises a polyurethane rubber material having a Shore D hardness in the range 50-60, and good resistance to abrasion.
To resist possible penetration of dirt, to abrade the composite material of the spring, the resilient element preferably extends, longitudinally of the spring, beyond the spring-engaging end of the component secured thereto.
The use of a locating element according to the invention is possible whether the component secured to the spring is an axle or associated part, or another composite spring. In the latter case, a further locating element of similar form to the first element may be used, engaging a depression in the further spring, with the body portions of the two locating elements co-operating with one another, either directly or by way of a spacer member between the springs.